Structural Optimization And Oxygenation Performance Studies Of Air-Forced Type Low-Pressure Jet Aeration

Aeration plays an important role in ensuring sludge activity in the aerobic tank of the sewage.At the same time,aeration is also the main energy consumption in the operation of the whole sewage treatment plant.The aeration system consumes the most energy in each process section of sewage treatment,accounting for about 55%to 60%of the total energy consumption.The volume of aeration mainly depends on the oxygen demand of the activated sludge and the oxygen transfer efficiency of the aeration device.Reducing the energy consumption of the aeration system without affecting the efficiency of sewage treatment is of great significance to the efficient operation and energy consumption of the sewage plant.In the process of engineering p ractice,energy conservation can be realized by reducing the oxygen demand of activated sludge,which may result in the risk of substandard sewage treatment due to decreased activity of activated sludge.In comparison,it is safer and more feasible to reduce the energy consumption of the aeration system by improving the oxygen transfer efficiency of the aerator.This paper aim to investigate the influence of some important factors on the oxygen mass transfer of air-forced type low-pressure jet aeration combining the Computed Fluid Dynamics?CFD?simulation and clean water oxygenation test.The main work and conclusions are as follows:?1?The three-dimensional model of the air-forced type low-pressure jet aerator was established by CFD,and the internal structure was optimized and simulated.Orthogonal experiments were designed for the factors affecting the mixing effect of gas-liquid two-phase turbulence?the primary nozzle diameter,the secondary nozzle diameter,the mixing chamber aspect ratio?,and the ex perimental results were analyzed by FLUENT simulation software.The results indicated that under the simulated conditions of 1.5 m·s^-1 for circulating water flow and 10 m·s^-1 for inlet flow rate respectively,,the order of factors affecting the mixing effect of gas-liquid two-phase turbulence was as follows:the primary nozzle diameter,the mixing chamber aspect ratio,the secondary nozzle diameter.The structural parameters for the optimal turbulent mixing effect were that the primary nozzle diameter of 14 mm,the secondary nozzle diameter of 46 mm,and the mixing chamber aspect ratio of 4.?2?CFD was used to study the turbulent mixing effect of gas-liquid two-phase on air-forced type low-pressure jet aeration with different operating parameters.The flow field information of the pressure field,velocity field and turbulent flow field inside the aeration was obtained and analyzed.Our findings thus revealed that the flow ratio was an important factor affecting the turbulent mixing effect of the gas-liquid two-phase in air-forced type low-pressure jet aeration.Under the condition of constant gas velocity,increasing the liquid velocity was more conducive to the mixing effect of the low-pressure jet aeration;Under the condition of constant liquid velocity,in creasing the gas velocity was not conducive to the mixing effect of the low-pressure jet aeration;Under the condition of constant gas water flow ratio,the absolute flow rate was more conducive to the mixing effect of low-pressure jet aeration.?3?The oxygenation performance test of jet aeration of different sizes was evaluated in reaction tank with an effective volume of 63 m³.The results showed that the total mass transfer coefficient of standard oxygen?K_La_s?and the standard oxygen mass transfer rate?SOTR?of jet aeration increased significantly with the increase of the gas flow,while the standard oxygen transfer efficiency?SOTE?reduced significantly;With the increase of circulating water volume,the standard oxygen total mass transfer coefficient?K_La_s?,the standard oxygen mass transfer rate?SOTR?and the standard oxygen transfer efficiency?SOTE?of the jet aerator increased significantly;With the increase of primary nozzle diameter of air-forced type low-pressure jet aeration,the standard oxygen total mass transfer coefficient?K_La_s?,the standard oxygen mass transfer rate?SOTR?,the standard oxygen transfer efficiency?SOTE?and the standard aeration efficiency?SAE?decreased,while the power consumption increased.In the case of the same gas-water ratio,the K_La_s,SOTR,SOTE and SAE of the simulated optimized structure of the jet aeration were improved by 68.84⁸8.77%,68.41⁹0.01%,68.41⁹3.19%and 48.96⁶7.03%respectively compared with the original structure.At a water depth of between 3 m and 5.5 m,the jet aeration exhibited excellent oxygenation capacity with the increase of effective water depth.